A turbogenerator with a shaft mounted permanent magnet motor/generator can be utilized to provide electrical power for a wide range of utility, commercial and industrial applications. While an individual permanent magnet turbogenerator may only generate 20 to 100 kilowatts, powerplants of up to 500 kilowatts or greater are possible by linking numerous permanent magnet turbogenerators together. Peak load shaving power, grid parallel power, standby power, and remote location (stand-alone) power are just some of the potential applications for which these lightweight, low noise, low cost, environmentally friendly, and thermally efficient units can be useful.
The conventional power control system for a turbogenerator produces constant frequency, three phase electrical power that closely approximates the electrical power produced by utility grids. Key aspects of such a power generation system are availability and reliability.
In grid-connect power generation, lack of availability can result in penalties from the local utility. Since many utility users are charged variable rates depending upon the amount of power drawn during a given period of time, the lowest $/kWh is charged when power is drawn at lower levels than some negotiated base. Power drawn above the base level will usually have greatly increased fees and sometimes a penalty associated with it. While grid-connect power generation can be used to provide less expensive power when more than the utility base level of power is required, should this grid-connect power generation fail, or otherwise be unavailable, greater costs to the user would ensue.
Availability and reliability are even more important in a standalone system in which the turbogenerator itself is providing the entire load for a user. If the turbogenerator is unavailable, lengthy interruptions to all aspects of a user's business can occur and result in significant financial loss to the user. For remote installations, the turbogenerator could be down for a long period of time since it might take a while for a service person to provide support at the remote site.
In a gas turbine engine, inlet air is continuously compressed, mixed with fuel in an inflammable proportion, and then contacted with an ignition source to ignite the mixture which will then continue to burn. The heat energy thus released then flows in the combustion gases to a turbine where it is converted to rotary energy for driving equipment such as an electrical generator. The combustion gases are then exhausted to atmosphere after giving up some of their remaining heat to the incoming air provided from the compressor.
Quantities of air greatly in excess of stoichiometric amounts are normally compressed and utilized to keep the combustor liner cool and dilute the combustor exhaust gases so as to avoid damage to the turbine nozzle and blades. Generally, primary sections of the combustor are operated near stoichiometric conditions which produce combustor gas temperatures up to approximately four thousand (4,000) degrees Fahrenheit. Further along the combustor, secondary air is admitted which raises the air-fuel ratio and lowers the gas temperatures so that the gases exiting the combustor are in the range of two thousand (2,000) degrees Fahrenheit.
It is well established that NOx formation is thermodynamically favored at high temperatures. Since the NOx formation reaction is so highly temperature dependent, decreasing the peak combustion temperature can provide an effective means of reducing NOx emissions from gas turbine engines as can limiting the residence time of the combustion products in the combustion zone. Operating the combustion process in a very lean condition (i.e., high excess air) is one of the simplest ways of achieving lower temperatures and hence lower NOx emissions. Very lean ignition and combustion, however, inevitably result in incomplete combustion and the attendant emissions which result therefrom. In addition, combustion processes are difficult to sustain at these extremely lean operating conditions.